docs: def _search_in_bases(type_):
      """Implementation detail."""
      found = False
      for base_type in type_.declaration.bases:
          try:
              found = internal_type_traits.get_by_name(
                  base_type.related_class, "element_type")
          except runtime_errors.declaration_not_found_t:
              pass
          if found:
              return found
      raise RuntimeError(
          ("Unable to find 'element_type' declaration '%s'"
           "in type '%s'.") % type_.decl_string)